The Molecular Cytogenetics Facility (MCF) provides basic and clinical investigators with conventional and FISH-based cytogenetic services. The goals of the core are to provide 1) high-quality, reasonably-priced cytogenetic services and expertise for requesting investigators;2) standard chromosome karyotyping and G, C, Q, R, silver staining to ascertain chromosomal abnormalities for evidence of genomic instability; 3) fluorescence in situ hybridization (FISH) of metaphase spreads using commercially- available chromosome paint probes, locus-specific probes, and telomere probes;4) Spectral Karyotyping (SKY) service to unambiguously identify, in one hybridization reaction, mouse or human chromosomal translocations present within a metaphase spread;5) specialized services, such as telomere length determination by Quantitative-FISH (Q-FISH), on an as-needed basis;and 6) access to personnel who are highly-experienced in a variety of cytogenetic technologies as well as access to the methodologies themselves. The MCF avoids expensive duplication in individual faculty laboratories of personnel, facilities, and equipment required for application of these powerful tools. The Facility occupies 250 sq. ft. within the Department of Cancer Genetics. An additional 200 sq. ft. microscope room houses 4 fluorescent microscopes for chromosomal analyses. The MCF is staffed with a Director, a Co-Director, 1 Laboratory Assistant, 'and a Professor Emeritus. During the previous funding period, 741 specimens were collected for both conventional and FISH-based cytogenetic services. Peer-funded investigators are given priority for MCF services that were used by 76 investigators from 18 of the 19 CCSG programs. 92% of users had peerreviewed funding and accounted for 85% of utilization. Since its inception, the MCF has successfully supported 5 peer-reviewed NIH-funded grants and investigators using data generated by the MCF have published extensively in top-tier journals. Future plans are to establish new cytogenetic services as well as to upgrade existing technologies.